No. 2 (192 1 ) REMARKS ON CANNING 85 



spoil the closing of solderless tins by undue or uneven pressure 

 in a badly adjusted machine. 



101. (7) Testing. — The success of the sealing operation is readily 

 tested. The closed cans are placed on edge in rows in wire 

 baskets and plunged into water kept at about l8o° to 200° F. ; the 

 temperature should be nearly that of boiling but without the 

 disturbance caused by ebullition. The strong heat of the water 

 expands any air within the can and, if there is even a minute 

 aperture, within a few seconds the air forces itself out in a con- 

 tinuous stream of bubbles which is readily detected; any such 

 can is at once lifted out with proper tongs, marked at the defective 

 spot and sent at once to the solderers for repair. If the tin is 

 solderless, a second passing through the double seamer may pos- 

 sibly cure the defect. There is no impropriety in passing cans as 

 good which have thus been reclosed before processing; the 

 leakage has not caused decomposition or been discovered by such 

 decomposition but is a mere petty defect in sealing discovered at 

 the very instant after sealing. Since each can bears the private 

 mark of the solderer who made the empty can as well as the 

 solderer who sealed the packed tin, the responsibility for bad 

 soldering is easily determined. It is here that the solid drawn 

 solderless cans have a great advantage over soldered tins, viz., 

 that there is only one seam to leak, that which unites body to 

 cover ; hence only one source of leaks as against three (top, bottom, 

 and side) in ordinary soldered cans. 



If no leaks are detected within a minute or so at a temperature 

 of or above l8o° F. the cans may be passed as prima facie sound. 



102. Canners are frequently puzzled by cans going wrong in 

 store, though they have successfully passed the testing vat. This 

 may be due to leaks from causes such as — 



(1) subsequent straining of the joint in processing or at the close 

 of processing (see below paragraphs 115 — 126 s.v. ' processing ') ; 



(2) weak soldering or the giving way of soldering at a rusty 

 point ; 



(3) a hole so minute that the pressure within the can has not 

 sufficed to drive the air visibly through it at the moderate tempera- 

 ture and consequent air pressure attained by the can in the testing 

 vat ; 



(4) a minute leak being temporarily closed by the expanded 

 air forcing into it a morsel of the contents ; 



4.A . - 



